From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 32B54C7EE2F for ; Mon, 5 Jun 2023 09:54:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230127AbjFEJyi (ORCPT ); Mon, 5 Jun 2023 05:54:38 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34564 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229579AbjFEJyf (ORCPT ); Mon, 5 Jun 2023 05:54:35 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 550BAD2; Mon, 5 Jun 2023 02:54:33 -0700 (PDT) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 22949D75; Mon, 5 Jun 2023 02:55:19 -0700 (PDT) Received: from FVFF77S0Q05N (unknown [10.57.24.244]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id A0CD03F793; Mon, 5 Jun 2023 02:54:31 -0700 (PDT) Date: Mon, 5 Jun 2023 10:54:26 +0100 From: Mark Rutland To: Ravi Bangoria Cc: Krzysztof Kozlowski , "Peter Zijlstra (Intel)" , jolsa@kernel.org, irogers@google.com, bp@alien8.de, adrian.hunter@intel.com, linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org, "linux-samsung-soc@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , "regressions@lists.linux.dev" Subject: Re: [REGRESSION][BISECT] perf/core: Remove pmu linear searching code Message-ID: References: <3abd3693-ad87-9abf-a762-337076638fcc@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jun 05, 2023 at 03:04:45PM +0530, Ravi Bangoria wrote: > On 05-Jun-23 12:40 PM, Mark Rutland wrote: > > On Sun, Jun 04, 2023 at 01:38:10PM +0200, Krzysztof Kozlowski wrote: > >> Hi, > >> > >> #regzbot introduced: 9551fbb64d09 > >> > >> Bisect pointed to commit 9551fbb64d09 ("perf/core: Remove pmu linear > >> searching code") as first one where all hardware events are gone from > >> perf for ARMv7 Exynos5422 board. > > > > I think that commit 9551fbb64d09 is just wrong. > > > > The commit message asserts: > > > > Searching for the right pmu by iterating over all pmus is no longer > > required since all pmus now *must* be present in the 'pmu_idr' list. > > So, remove linear searching code. > > > > ... and while each PMU has *some* entry in the pmu_idr list, for its dynamic > > type, that means that events with other types (e.g. PERF_TYPE_HARDWARE or > > PERF_TYPE_RAW) will fail to find a PMU in the IDR whereas they'd previously > > have been accepted by a PMU during the subsequent iteration over all PMUs. > > Not sure I follow. > > PERF_TYPE_HARDWARE and PERF_TYPE_HW_CACHE are aliased to PERF_TYPE_RAW in > perf_init_event(). And PERF_TYPE_RAW should be present in pmu_idr if it > was registered using: > > perf_pmu_register(pmu, "name", PERF_TYPE_RAW); As I said, the PMUs get registered with a dynamic type, and there's no registration with PERF_TYPE_RAW. On arm/arm64 systems, *every* CPU PMU gets registered with: perf_pmu_register(pmu, name, -1); ... and *none* are registered with: perf_pmu_register(pmu, name, PERF_TYPE_RAW) ... so those all get a dynamic IDR type, and nothing gets placed into the IDR for PERF_TYPE_RAW, etc. We rely on the linear search to find a PMU that can handle PERF_TYPE_RAW, etc. I appreciate that's not ideal, but it's how it has worked for almost a decade now, so we can't change the userspace-visible behaviour. Thanks, Mark.